To provide a knockdown steel pipe and a concrete-filled steel pipe using the steel pipe, easy in assembling into a cylindrical shape even in a large diameter steel pipe, and easily equalizing yield strength of a joint part to a steel pipe peripheral wall part.

This knockdown steel pipe has joint piece parts 12a and 12b on both edges on the cylindrical body peripheral directional side of steel pipe peripheral wall constituting members 11a and 11b in the shape of longitudinally splitting a cylindrical body into a plurality; and is formed in a cylindrical shape by joining its joint piece parts in a state of being superposed on the inside and outside of the cylindrical body; and is superposed in a state of fitting a projection strip and a recessed groove turned in the cylindrical body axis direction to both contact planes superposed on the inside and outside of the cylindrical body. Its superposed part is integrated by a bolt 17. The concrete-filled steel pipe is formed by filling concrete 32 in this cylindrical knockdown steel pipe.